父指针和孩子链表法：

#include <bits/stdc++.h>
using namespace std;
vector<int> fa;
vector<int> child[101];
int main(){
    int n,m,x,y;
    cin>>n>>m;
    fa.resize(n+1,0);
    for(int i=0;i<m;i++){
    	cin>>x>>y;
    	child[x].push_back(y);
    	fa[y]=x;
	}
     int maxcnt=0,maxnode=0;
     for(int i=1;i<=n;i++){
     	if(fa[i]==0) 
     	   cout<<i<<endl;
     	if(child[i].size()>maxcnt){
     		maxcnt = child[i].size();
     		maxnode= i;
		 }
	 }
	 cout<<maxnode<<endl;
	 for(auto x :child[maxnode]) {
	 	 cout<<x<<" ";
	 }
	return 0;
}